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Yacht Modems Let Fans Keep Track of Races Online

ARMCHAIR sailors will be able to follow the America's Cup yachting race from both their television sets and their computers, thanks to a new system that receives data from wireless modems aboard the yachts.

The system, developed by the Electronic Company of New Zealand and Telecom New Zealand, is in place now and broadcasting the Louis Vuitton Cup, in which 11 teams participate in a series of round robin races for the chance to compete against Team New Zealand, the Cup defenders.

Each yacht in the race carries a Global Positioning System device, which constantly monitors its latitude and longitude. A Sierra Wireless MP200 cellular modem, built to withstand heavy vibration, is also mounted on each yacht. Similar modems are zipped into inflatable pouches on marker buoys along the course, 18 1/2 nautical miles.

As the yachts move through the course, the modems transmit multiple streams of information -- G.P.S. location data as well as data on wind speed and direction -- to Animation Research, a New Zealand graphics company. The transmissions will occur two times each second during the qualifying races, and five times each second during the America's Cup. The information is then translated into an animated simulation of the yachts at sea on a television or computer screen.

The animation program, which will be featured on ESPN, was originally developed to give TV viewers a better perception of the yachts' progress, said Tony Thomas, chief executive of the America's Cup. For $70, America's Cup fans who visit www .americascup.org can purchase the Virtual Spectator animation CD package and use it to translate race updates as they are transmitted over the Internet. They can also download and watch races that already occurred.

''It's often difficult to tell which yacht is ahead by watching video footage,'' he said. ''We wanted to educate the viewers as to exactly where the yacht is in relation to the finish mark.'' Dotted lines and flowing arrows on the screen also indicate the distances between two yachts; their trails; which direction they are moving in, in relation to the finish mark; the distance to the finish mark and the wind direction.

When the Young America yacht split in half on Nov. 9 while racing Nippon of Japan, for example, a dot flashed in place while Nippon's dot Nippon moved up the screen.

There was some initial concern among race participants when the modems were installed that another team could use some of the transmitted information. If one yacht was able to learn of another yacht's speed during its trajectory into and away from the wind toward the final mark, (which is known as optimum velocity made good), it could develop its own course based on that information. ''You wouldn't want another yacht to know what speed you're going for,'' said Dawn Riley, captain of America True, the team representing the San Francisco Yacht Club. ''It's kind of like stealing a playbook.''

As a result, slight distortions are created in the information that is relayed from the yachts. If the G.P.S. data, for example, show a yacht traversing an ocean swell, the program might depict it moving across a flat surface. The effect is an accurate enough simulation for racing fans, but the graphics are not technical enough to reveal anything significant to a competing team.

But even with distortions, some of the teams view and rehash the recorded races after they are over. ''We use it to analyze our tactics,'' Ms. Riley said. ''It gives us an idea of when we were doing well against the other yachts, and when we weren't.''